I'm only curious about the relationship between what is still in the original input signal into the lathe and what distortion gets added. Even if it is rolled off, a bunch of HF distortion is added, it seems.

I'm only curious about the relationship between what is still in the original input signal into the lathe and what distortion gets added. Even if it is rolled off, a bunch of HF distortion is added, it seems.

Ah, I'd seen that. Unfortunately, there are ways I can think of it as being not so definitive. The cutoff is apparent, but you can also see there is distortion added. In some transients they seem to blend together on the graph, and other times we see varying amounts of a difference between the frequencies right before the cutoff and right after (a sharp drop).

Needless to say, it shows that there is definitely useful info above 20kHz, but that there is also a good amount distortion up there too. Some relationship between the two, possibly also including the level. That comment also links an interesting article! I wonder at what level the bias tone would be at...

I'm only curious about the relationship between what is still in the original input signal into the lathe and what distortion gets added. Even if it is rolled off, a bunch of HF distortion is added, it seems.

Distortion during LP playback rises with frequency for reasons relating to groove geometry. When there was a desire to exploit response > 20 KHz for quadraphonic music, actually recovering even just a pilot tone from up there was a challenge, and this is the easier part of the problem of recovering music with acceptable sound. Not only that, but the durability of this ultrasonic information was widely reported to be poor. Maybe 10 more or less playings would erase the music.